Electron Cooling for High Luminosity Electron-Ion

Collider at JLab Ya. Derbenev, P. Evtushenko, and Y. Zhang

Cool’09 WorkshopLanzhou, China, August 31 to September 4, 2009

Outline• Introduction

• Forming and Cooling of High Intensity Ion Beams in ELIC

• Conceptual Design of ERL Based Circulator Electron Cooler

• Key Enabling Technologies and R&D

• Summary

1. Introduction

Nuclear Physics Program at JLab

TODAY: 6 GeV CEBAF

• One of two primary US nuclear science research centers funded by US DOE

• It operates CEBAF, the world-first high energy SRF recirculated electron linac

• CEBAF delivers 6 GeV polarized CW beam to three fixed targets (experimental halls)

Recirculated Linac

Three Experimental Hall

11 GeV max energy

12 GeV max energy

Nuclear Physics Program at JLab

Tomorrow: CEBAF Energy Upgrade & Science Beyond 2025

12 GeV CEBAF Upgrade A $340M energy doubling CD3 approved, construction already started Construction will be completed by 2014(?),

science will start after 6 month commission Exciting fixed target program beyond 2020

What upgraded CEBAF will provide Up to 12 GeV CW electron beam High repetition rate (3x499 MHz) High polarization (>80%) Very good beam quality

Opportunity: Electron-Ion Collider on CEBAF Add a modern ion complex with a Green Field design Expand science program beyond 12 GeV CEBAF fixed target Open up new science domain with higher CM energy

Nuclear Physics Program at JLabDay After Tomorrow: Electron-ion Collider

at JLab & Science Beyond 2040

WM

SURA

City of NN

State

City of NN

ELIC Footprint (~1800m)

MEIC Footprint (~600m)

CEBAF

Three compact rings:• 3 to 11 GeV electron• Up to 12 GeV/c proton

(worm)• Up to 60 GeV/c proton (cold)

EIC@JLab: Low to Medium Energy

polarimetry

EIC @ JLab: High Energy & Staging

Ion Sources

SRF Linac

p

e

e e

pp

prebooster

ELIC collider

ring

MEIC collider

ring

injector

12 GeV CEBAF

Ion ring

electron ring

Vertical crossing

Interaction Point

Small

Circumference m 1800

Radius m 140

Width m 280

Length m 695

Straight m 306

Stage Max. Energy (GeV/c)

Ring Size (M)

Ring Type IP#

p e p e p e

1 Low 12 5 (11) 630 630 Warm Warm 1

Medium 60 5 (11) 630 630 Cold Warm 2

2 Medium 60 10 600 1800 Cold Warm 4

3 High 250 10 1800 1800 Cold Warm 4

EIC@JLab Parameters Beam Energy GeV 250/10 150/7 60/5 60/3 12/3Collision freq. MHz 499Particles/bunch 1010 1.1/3.1 0.5/3.25 0.74/2.9 1.1/6 0.47/2.3Beam current A 0.9/2.5 0.4/2.6 0.59/2.3 0.86/4.8 0.37/2.7Energy spread 10-4 ~ 3RMS bunch length mm 5 5 5 5 50Horz. emit., norm. μm 0.7/51 0.5/43 0.56/85 0.8/75 0.18/80Vert. emit. Norm. μm 0.03/2 0.03/2.87 0.11/17 0.8/75 0.18/80Horizontal beta-star mm 125 75 25 25 5Vertical beta-star mm 5Vert. b-b tuneshift/IP 0.01/0.1 0.015/.05 0.01/0.03 .015/.08 .015/.013Laslett tune shift p-beam 0.1 0.1 0.1 0.054 0.1

Peak Lumi/IP, 1034 cm-2s-1 11 4.1 1.9 4.0 0.59

High energy Medium energy Low energy

Current focus

Achieving High LuminosityELIC design luminosity

L~ 1035 cm-2 s-1 for high energy (250 GeV x 10 GeV)

L~ 4x1034 cm-2 s-1 for medium energy (60 GeV x 3 GeV)

ELIC luminosity Concepts• High bunch collision frequency (0.5 GHz, can be up to 1.5 GHz)• Short ion bunches (σz ~ 5 mm) (also much smaller bunch charge)• Relative long bunch (comparing to beta-star) for very low ion energy• Strong final focusing (β*y ~ 5 mm)• Large beam-beam parameters (~0.01/0.1, 0.025/.1 largest

achieved)

• Need electron cooling of ion beams• Need crab crossing colliding beams

• Large synchrotron tunes to suppress synchrotron-betatron resonances

• Equal (fractional) betatron phase advance between IPs

2. Forming and Cooling of High Intensity Ion Beams in ELIC

Length (m)

Max. Energy (GeV/c)

Cooling Scheme Process

Source/SRF linac 0.2 Full strippingAccumulator-Cooler Ring

(Pre-booster) ~100 3 DC electron

Stacking/accumulatingEnergy boosting

Low energy ring(booster) ~630 12 Electron

(ERL)Fill ring/Energy boosting

RF bunching (for collision)Medium energy ring

(large booster) ~630 60 Electron (ERL)

Energy boostingRF bunching (for collision)

High energy ring ~1800 250 Electron (ERL)

Fill ring/energy boostingRF bunching

source

SRF Linac

pre-booster-Accumulator

ring Booster-low energy collider ring

Medium energy ion collider ring

To high energy ion collider ring

(for Full Energy EIC@JLab)

cooling

Forming High Intensity Ion Beam With Staged Cooling

Stacking/cooling Ion Beam in Pre-booster/Accumulator Ring

• Accumulation of 1 A coasted beam in pre-booster • Polarized p, d: stripping injection from negative ion source after linac• Other ions: must use DC electron cooling

– Multi-turn (~10) pulse injection from linac– Damping/cooling of injected pulse– Accumulating beam at space charge limited emittance

• Accelerating to 3 GeV/c • Fill large booster/low energy collider ring, then accelerate• Switch to collider ring for energy booster,• RF bunching and initial/continuous cooing

Circumference M ~80Arc radius M ~3Crossing straight length M 2 x 15Energy/u GeV 0.2 -0.4Electron current A 1Electron energy MeV 0.1 - 0.2Cooling time for protons ms 10Stacked ion current A 1Norm. emit. After stacking µm 16

An advanced conceptOvercoming space charge by accumulating low temperature, large area beam in ring with circular betatron modes

Pre-booster/Accumulator-ring

Initial, Final and Continuous Cooling of Ion Beam in Collider Ring

GeV/MeV Initial Cooling

after bunching & boost

Colliding Mode

Momentum GeV/MeV 12 / 6.55 60 / 32.67 60 / 32.67Beam current A 0.6 / 3 0.6 / 3 0.6/ 3Particles/Bunch 1010 0.74 / 3.75 0.74 / 3.75 0.74 / 3.75Bunch length mm 200 / 200

(coasted)10 / 30 5 / 15

Momentum spread 10-4 5 / 1 5 / 1 3 / 1Horizontal emittance, norm. µm 4 1 0.56Vertical emittance, norm. µm 4 1 0.11Laslett’s tune shift (proton) 0.002 0.006 0.1Cooling length/circumference m/m 15 / 640 15 / 640 15 / 640Cooling time s 92 162 0.2IBS growth time (longitudinal) s 0.9

Advanced Concepts of Electron Cooling• Staged cooling

– Start (longitudinal) electron cooling at injection energy in collider ring– Continue electron cooling after acceleration to high energy

• Sweep cooling – After transverse stochastic cooling, ion beam has a small transverse temperature but

large longitudinal one. – Use sweep cooling to gain a factor of longitudinal cooling time

• Dispersive cooling – compensates for lack of transverse cooling rate at high energies due to large transverse

velocity spread compared to the longitudinal (in rest frame) caused by IBS• Flat beam cooling (for high energies)

– based on flattening ion beam by reduction of coupling around the ring – IBS rate at equilibrium reduced compared to cooling rate

• Matched cooling (low energies)– based on use of circular modes optics of ions matched with solenoid of cooling section– separates cooling of beam temperature from cooling (round) beam area– results in removal temperature limit due to space charge (strong reduction of achievable

4D emittance)

Flat-to-Round Beam Transform and Reduction of Space Charge

• Flat colliding ion beam and space charge• Colliding ion beam should be flat at interaction point in order to match flat

electron beam (due to synchrotron radiation)• Space charge tune shift is a leading limiting factor for low energy ion beam,

and it further effect luminosity of the collider• Flat beam enhances space charge tune-shift . i.e., Laslett tune-shift is

determined by smaller transverse dimension

• Luminosity optimization: flat-to-round transform if colliding ion beam can be arranged as

• flat at interaction point matching flat electron beam• Round in the storage maintaining large transverse beam area

for overcoming space charge

• Technical feasibility• circular (100% coupled) optics (ring) under matched cooling• Special adapters to converting round beam to flat beam and back to round

beam at collision point

3. Conceptual Design of ERL Based Circulator Electron Cooler

Design of e-Cooler for EIC@JLabDesign Requirements and Challenges

• Electron beam current• up to 3 A CW beam at 499 MHz repetition rate• About 5 nC bunch charge (possible space charge issue at low energy)• About 260 kC per day from source/injector (state-of-art is 0.2 kC per day)

• Energy of cooling electron beam• up to 6.7 MeV for cooling low energy (12 GeV/c) ELIC• up to 33 MeV for cooling medium energy (60 GeV/c) ELIC• up to 136 MeV for cooling high energy (250 GeV/c) ELIC

• Beam power• Need 100 to 400 MW for cooling 60 to 250 GeV/c ELIC

Design Choice: ERL Based Circulator Cooler (ERL-CCR)• Energy Recovery SRF Linac (ERL) to solve RF power problem• Circulator-cooler ring (CCR) for reducing average current from source/ERL

ERL-CCR can provide the required high cooling current while consuming fairly low RF power!

Conceptual Design of Circulator e-Cooler

ion bunch

electron bunch

Electron circulator

ringCooling section

solenoid

Fast beam kicker

Fast beam kicker

SRF Linac

dumpelectron injector

energy recovery

path

Circulator ring by-pass

Path length adjustment

(synchronization)

ELIC e-Cooler Design ParametersMax/min energy of e-beam MeV 33/8Electrons/bunch 1010 3.75bunch revolutions in CCR ~300Current in CCR/ERL A 3/0.01Bunch repetition in CCR/ERL MHz 500/1.67CCR circumference m 80Cooling section length m 15Circulation duration s 27Bunch length cm 1-3Energy spread 10-4 1-3Solenoid field in cooling section T 2Beam radius in solenoid mm ~1Beta-function m 0.5Thermal cyclotron radius m 2Beam radius at cathode mm 3Solenoid field at cathode KG 2Laslett’s tune shift @60 MeV 0.07Longitudinal inter/intra beam heating

s 200

• Number of turns in circulator cooler ring is determined by degradation of electron beam quality caused by inter/intra beam heating up and space charge effect.

• Space charge effect could be a leading issue when electron beam energy is low.

• It is estimated that beam quality (as well as cooling efficiency) is still good enough after 100 to 300 turns in circulator ring.

• This leads directly to a 100 to 300 times saving of electron currents from the source/injector and ERL.

Electron Source/Injector• ELIC CCR driving injector

10 mA@1.667 MHz, up to 33 (125) MeV energy 5 nC bunch charge, magnetized

• Challenges Source life time: 0.86 kC/day (state-of-art is 0.2 kC/day)

source R&D, & exploiting possibility of increasing evolutions in CCR • Conceptual design

High current/brightness source/injector is a key issue of ERL based light source applications, much R&D has been done

We adopt light source injector as a baseline design of CCR driving injector • Beam qualities should satisfy electron cooling requirements (based on previous

computer simulations/optimization) • Bunch compression may be needed.

300keV DC gun

solenoids

buncher

SRF modules

quads

Circulator Ring & Synchronization

Transverse focusing

lattice

Synchronization• Bunch spacing depends on

beam energy. There is about 1.8 mm difference when energy is boosted from 12 to 60 GeV/c

• A 10m dog-lag lattice or loops in arc must be introduced to ensure electron-ion synchronization at cooling section.

• Maximum deflecting angle is 13º, providing total 26cm path length adjustment.

Bunch In/out kicking • An ultra fast kicker switches

electron bunches in and out circulator ring.

• Deflecting angle should be large enough to separate outgoing bunches from circulating bunches and be further deflected by a dipole

• Duration of kicking should be less than bunch spacing (~1/500MHz = 2 ns)

energy MeV 33Kick angle 0.04Integrated BDL GM 400Frequency BW GHz 2Kicker aperture cm 2Repetition Rate MHz 1.67Power kW 13

Kicker Parameter

4. Key Enabling Technologies and Critical R&D

Energy Recovery Linac

• SRF ERL based FEL • High average power, up to14 kW (world record)• mid-infrared spectral region• Extension to 250 nm in the UV is planned• Photocathode DC injector, 10 mA class CW

beam, sub-nC bunch charge• Beam energy up to 200 MeV, energy recovery• Next proposal: 100kW average power, 100

mA CW beam. ERL, nC-class bunch charge

JLab FEL Program

Energy Recovery

Energy MeV 80-200Charge/bunch pC 135Average current mA 10Peak current A 270Beam power MW 2Energy spread % 0.5Normalized emittance µm-rad <30

JLab is world leader in ERL technology !

Test Facility for Circulator Cooling Ring

• Proposal for a test facility of a ERL based circulator cooler utilizing existing JLab FEL facility is under consideration. Additional hardware cost is moderate.

• Focusing of this test facility will be studies of – Lifetime of driving high peak current/bunch charge source/injector– beam dynamics of high bunch charge electron beam in the circulator ring

(space charge effect, IBS heating up, etc.)– test of fast kicker.

Transverse focusing

lattice

Diagnostic element

Using JLab FEL ERL facility or a new SRF module

Ultra-Fast Kicker based on a Flat Kicking Beam

h

v0

v≈csurface charge density

F

L

σc

Dkicking beam

• A short (1~ 3 cm) target electron bunch passes through a long (15 ~ 50 cm) low-energy flat bunch at a very close distance, receiving a transverse kick

• The kicking force is

integrating it over whole kicking bunching gives the total transverse momentum kick

• Proof-of-principle test of this fast kicker idea can be planned. Simulation studies will be initiated.

)1(2 0

0

eeF

Circulating beam energy MeV 33Kicking beam energy MeV ~0.3Repetition frequency MHz 5 -15Kicking angle mrad 0.2Kinking bunch length cm 15~50Kinking bunch width cm 0.5Bunch charge nC 2 An ultra-fast RF kicker is

also under development.

V. Shiltsev, NIM 1996

Summary• EIC@JLab promises to accelerate a wide variety of ions to collider with

electron/positron beam with a CM energy range from 10 to 100 GeV, enabling a unique physics program in a coherent way.

• ELIC Luminosity should be able to reach 4x1034 cm-2s-1 at medium energy (60x3~5 GeV2) for e-p collisions, achieved through a very strong vertical final focusing (β*=5mm) of a high repetition CW ion beam of very short bunch length (~5mm) and very small transverse emittance.

• Electron cooling is essential for forming (through stacking & accumulating) and cooling of the high intensity ion beam for ELIC.

• Conceptual design of an ERL circulator-ring based electron cooler has been proposed to provide high intensity (3 A) and high energy (up to 137 MeV) cooling electron beam.

• Key enabling technologies and critical RD on ERL, circulator ring, high bunch charge electron source and ultra-fast kicker are also discussed and planed.

Backup Slides

ELIC Study Group A. Afanasev, A. Bogacz, J. Benesch, P. Brindza, A. Bruell, L. Cardman, Y.

Chao, S. Chattopadhyay, E. Chudakov, P. Degtiarenko, J. Delayen, Ya. Derbenev, R. Ent, P. Evtushenko, A. Freyberger, D. Gaskell, J. Grames, L. Harwood, T. Horn, A. Hutton, C. Hyde, R. Kazimi, F. Klein, G. A. Krafft, R. Li, L. Merminga, J. Musson, A. Nadel-Turonski, M. Poelker, R. Rimmer, C. Tengsirivattana, A. Thomas, M. Tiefenback, H. Wang, C. Weiss, B. Wojtsekhowski, B. Yunn, Y. Zhang - Jefferson Laboratory staffs and users W. Fischer, C. Montag - Brookhaven National LaboratoryV. Danilov - Oak Ridge National Laboratory V. Dudnikov - Brookhaven Technology GroupP. Ostroumov - Argonne National LaboratoryV. Derenchuk - Indiana University Cyclotron FacilityA. Belov - Institute of Nuclear Research, Moscow, Rssia V. Shemelin - Cornell University

EnergyWide CM energy range between 10 GeV and 100 GeV• High energy: up to 10 GeV e on 250 GeV p or 100 GeV/n ion• Medium energy: up to 11 GeV e on 60 GeV p or 30 GeV/n ion• Low energy: 3 to 10 GeV e on 3 to 12 GeV/c p (and ion)

Luminosity • 1033 up to 1035 cm-2 s-1 per interaction point• Multiple interaction points

Ion Species• Polarized H, D, 3He, possibly Li• Up to heavy ion A = 208, all striped

Polarization• Longitudinal at the IP for both beams, transverse of ions• Spin-flip of both beams• All polarizations >70% desirable

Positron Beam desirable

ELIC Design Goals

Design ChallengesDesign an Electron-Ion Collider that

• Covers a very wide CM energy range (10 to 100 GeV) in a unified & coherent way for highest science productivity

• Deliver best collider quality in terms of high luminosity, high polarization, multiple interaction points, maximum flexibility and reliability

• Takes maximum advantage of existing CEBAF

• Offers a good path for staging and future upgrade

• Requires minimum R&D

• Realizes in a most cost effective way

ELIC Ring-Ring Design Features Unprecedented high luminosity Electron cooling is an essential part of ELIC Up to four IPs (detectors) for high science productivity “Figure-8” ion and lepton storage rings

Ensure spin preservation and ease of spin manipulation No spin sensitivity to energy for all species.

Present CEBAF injector meets storage-ring requirements 12 GeV CEBAF can serve as a full energy injector to electron ring Simultaneous operation of collider & CEBAF fixed target program. Experiments with polarized positron beam are possible.